The present invention relates to valve control systems for internal combustion engines, and more particularly, to an improved rocker arm assembly for use therein.
Valve control systems for engine poppet valves are generally well known in the art. Although not so limited, the present invention is especially adapted for use in valve control systems of the overhead cam (OHC) type, and will be described in connection therewith. In a typical OHC type of valve control system, there is provided, in addition to the engine poppet valve being controlled, a rocker arm assembly, and some sort of “fulcrum” mechanism about which the rocker arm assembly pivots. In addition, an OHC valve control system includes a camshaft defining a cam profile, and the rocker arm assembly includes a cam follower, such as a roller follower member rotatably disposed about, and supported on a shaft, with the shaft being fixed relative to the rocker arm assembly.
Typically, such rocker arm assemblies, of the type to which the present invention relates, include an integrally-formed valve tip pad portion to engage the upper stem tip portion of the engine poppet valve. The recent trend has been away from such integral valve tip pad portions, and toward the use of rotatable (pivotable) pad portions which can engage the stem tip, without sliding engagement therebetween. For example, U.S. Pat. No. 5,655,490 illustrates a number of different configuration types and mounting arrangements for stem tip pad portions. Among the various pad portion configurations shown in the cited patent are several which are of the “notched-log” type, i.e., they are generally cylindrical in overall configuration, but toward the center, are notched to define one or more flat surfaces, one of which is especially adapted for  engaging the end surface of the stem tip portion. Thus, although the present invention is not limited to this particular configuration of stem tip pad portion, or to any other particular configuration, except as is noted in the appended claims, the “notched-log” configuration does represent one preferred embodiment, and the invention will be described in connection therewith.
Although many valve control systems for internal combustion engine poppet valves are of the conventional, fixed type (i.e., having no capability of varying the valve lift or “deactivating” the engine poppet valve), and the invention may be used advantageously in such “fixed” valve control systems, the invention is especially adapted for use in deactivating valve control systems, and will be described in connection therewith. Although the various structures utilized to achieve valve deactivation are not essential to, and not even especially relevant to the present invention, and therefore will be described only briefly herein, there is one aspect of the typical valve deactivation system which is relevant to the present invention. Whereas, in a typical “fixed” valve control system, the rocker arm might pivot through an angle of only about 10 to 20 degrees, in a typical valve deactivating system, the rocker arm assembly typically pivots through an angle of as much as 25 degrees.
The need to maintain non-sliding engagement between the end surface of the valve stem tip portion and the rocker arm pad portion, through a relatively greater range of pivoting motion of the rocker arm (in the case of valve deactivation), somewhat complicates the provision of an appropriate valve tip pad portion, and the mounting of, and retention of the pad portion within the rocker arm assembly.
As is well known to those skilled in the art, the provision of a rotatable (or pivotable) pad portion which must be retained within the rocker arm assembly, in addition to the presence of the cam follower which is mounted on a shaft, and which must also be retained relative to the rocker arm assembly, adds substantially to the number of parts included in the overall rocker arm assembly. The necessary retention of the pad portion and the cam follower  shaft also add substantially to the overall manufacturing expense of the rocker arm assembly, and especially, the time and expense of assembling the rocker arm.